1. Field of the Invention
The present invention relates to a foldable pneumatic tire mainly used for a spare tire for vehicles such as automobiles.
2. Description of the Prior Art:
A foldable tire generally has foldable sidewalls. Such a tire has substantially the same dimension as in a normal tire when in use, but can be collapsed into a very small dimension so as to be housed in a spare housing when in an unused or deflated condition. Such tires have been known as disclosed in U.S. Pat. No. 3,347,300 and Japanese Patent Application Publication No. 35,957/75.
The tire disclosed in the U.S. Pat. No. 3,347,300 is molded and vulcanized in a mold whose cavity corresponds to that of the deflated or collapsed tire. In order to vulcanize the tire in the collapsed shape, a corresponding particularly shaped mold is used and bagless vulcanization is employed wherein the vulcanizing heat medium should be directly in contact with the tire to be vulcanized. Therefore, the tires according to the U.S. Pat. No. 3,347,300 require extensive modification of existing apparatuses and installations. Furthermore bagless vulcanization is generally prone to produce inferior tires that are rejected.
The Japanese Patent Application Publication No. 35,957/75 dicloses a foldable tire produced by existing apparatuses and installations used for normal tires requiring only a mold particular in shape without using any special equipment and methods. However, when vulcanized, there is a tendency for rubber material of a bent portion of a sidewall of the tire to be withdrawn into both sides thereof so as to become much thinner. In order to maintain the bent portion of the tire at a determined thickness, it is required to make thicker the sidewalls and rim cushions. However, thicker rim cushions of tire make it difficult to fit the tire onto the rim. In addition, the bent portion of the tire disclosed in the Publication makes it difficult to separate the tire from the vulcanizing mold when taking the vulcanized tire out of the mold after vulcanization and thus to decrease the productivity of tires considerably
U.S. Pat. No. 3,540,510 discloses a foldable tire produced by a method similar to that of the Japanese Patent Application Publication No. 35,957/75. In the tire disclosed in this U.S. Patent, a difference in thickness between the tread and rim cushion is present, so that the tire has less foldability and is difficult in rim assembly and hence very much inferior as an article to be produced.